Materials having surfaces decorated with metal nanoparticles are substrates common in many industrial applications. The areas of applications are strictly dependent on the nature of both the nanoparticles and the surface of the substrate.
Substrates consisting of polystyrene microspheres decorated on the surface with metal nanoparticles have been widely studied in the literature.
M. Bradley reports the use of such materials as catalysts for intracellular enzymatic reaction (R. Yusop, A. U. Broceta, E. M. V. Johansson R M Sanchez-Martin and M. Bradley palladium-mediated intracellular nature chemistry vol 3 (2011) 239-243).
These polymeric microspheres are widely used in the biomedical field. Saralidze et al. show the relationship between the various methods of synthesis of the microspheres and application areas. (K. Saralidze, L H Koole and M L W Knetsch. Polymeric Microspheres for Medical Applications Materials, 3 (2010) 3537-3564).
L. Xianqiao in his paper reports the application of polymeric microspheres decorated with magnetic nanoparticles for applications in the field of purification of antibodies (Xianqiao L., G. Yueping, Yueping Y., Yu, M. Zhiya, W. Xiaobing, L. Huizhou. Preparation of superparamagnetic immunomicrosphere and application for antibody purification J. Appl. Polym. Sci. 94 (2004) 2205-2211).
Substrates made of semiconductor materials decorated on the surface with metal nanoparticles have been found of great interest for applications in the environmental field thanks to their technological properties. In this regard, S. Kochuveedu shows the photocatalytic activity of TiO2 nanospheres decorated with Au nanoparticles for the oxidation of volatile organic compounds (Saji Thomas Kochuveedu, Dong-Pyo Kim, and Dong Ha Kim, Surface-Plasmon-Induced Visible Light photocatalytic Activity of TiO2 Nanospheres Decorated by Au Nanoparticles with Controlled Configuration. J. Phys. Chem. C 2012, 116, 2500-2506).
In order to obtain antibacterial and bacteriostatic fibers or textiles for various commercial products such as plasters, bandages, coats, pillows, socks, underwear etc., fibers are chemical treated to allow the deposition of metal nanoparticles on the fiber or the fabric textiles surface.
For this purpose, silver is the most used metal for this kind of applications. B. Filipowska in his work describes the manufacturing of cotton fibers decorated with metal nanoparticles of silver and demonstrates their particular antibacterial and antifungal properties (Filipowska B. et al, New Method for the antibacterial and antifungal modification of silver finished textiles & fibers textiles in eastern Europe 2011, Vol 19 4 (87) 124-128).
Several substrates properly surface-decorated with metal nanoparticles have important optical properties and find wide applications in the sensing area.
For example, carbon nanotubes surface-decorated with metal nanoparticles are widely used in the field of optical devices, sensors and as photovoltaic materials.
Prakash in his publication demonstrates how the introduction of metal nanoparticles in the heterogeneous organic/inorganic junction of solar cells, consisting of carbon nanotubes, increases the yield of the photovoltaic system (Prakash R. Somani, Savita P. Somani, and M. Umeno Application of metal nanoparticles decorated carbon nanotubes in photovoltaics Applied Physics Letters Vol. 93 (3) 2008).
Frank, in a 2004 work, shows the preparation of silica microspheres decorated with gold nanoparticles for an application in the field of chemical sensing (O. Frank, H. Hiroki, P. Rhiannon, G. Ting, Alkanethiol-induced structural rearrangements in silica-gold core-shell-type nanoparticle clusters: an opportunity for chemical sensor engineering, Langmuir 20 (2004) 5553-5558).
The preparation of substrates, surface-decorated with metal nanoparticles, can be carried out with a top-down or bottom-up approach.
In the “top-down” approach, nano-dimensional materials like nanoparticles can be produced by physical methods such as photolithography, electron beam lithography, milling or attrition from macroscopic materials (Gao, G., Nanostructures and nanomaterials. Synthesis, Properties & Applications. London: Imperial College Press, 2004).
In the “bottom-up” approach, nanoparticles are produced from molecular precursors by means of chemical processes. The typical techniques of this approach are nanosphere lithography, templating, chemical reduction, electrochemical reactions and sonochemical reactions.
In the bottom-up approach, nanoparticles originate from chemical precursors by means of processes of nucleation and growth of the crystal lattice (Tolaymat, T., El Badawy, A., Genaidy, A., Scheckel, K., Luxton, T., Suidan, M., An evidence-based environmental perspective of manufactured silver nanoparticle in syntheses and applications: a systematic review and critical appraisal of peer-reviewed scientific papers Sci. Tot. Environ., (408) 5, (2010) 999-1006).
It has been shown that the use of protective agents (capping agents) in the preparation of nanoparticles in the bottom-up method is often necessary for tuning the size, shape and stability of nanoparticles, but the result is the coating of a metal surface, changing the reactivity and the physical-chemical properties of nanoparticles (S. Scire', S. Giuffrida, C. Crisafulli, P M Riccobene, A. Pistone, Journal of Molecular Catalysis A: Chemical, 353-354 (2012) 87-94 and Balan, L., Malval, J., Schneider, R., Burget, D., Mater. Chem. Phys, 104 (2007) 417-21).
The conventional methods for the preparation of surfaces decorated with metallic nanoparticles are based on a bottom-up approach and consist in the pre-formation of metal nanoparticles, through thermal or photochemical chemical reduction, and the subsequent process of interaction adhesion with the surface of the substrate.
The following references report the state of the art of conventional methods for the preparation of decorated surfaces with metallic nanoparticles.
U.S. Pat. No. 7,666,494 B2 (D J McClure and M A Perez) reports a vapor phase method for the preparation of a monolayer of metal nanoparticles.
Filipowska B. et al, New Method for the antibacterial and antifungal modification of silver finished textiles fibers & textiles in eastern Europe, Vol 19 4-87 (2011) 124-128, describes the manufacturing of textile fibers decorated with silver nanoparticles.
US 2011/0110999 A1 describes a method for the deposition of preformed silver nanoparticles on the surface of natural and synthetic textile fibers.
U.S. Pat. No. 4,772,150 B2 describes a method for the preparation of porous surfaces decorated with metal nanoparticles; this method provides for the direct contact between a suspension of preformed nanoparticles with the porous surface of the substrate, and in such conditions the nanoparticles, only if of a suitable size, diffuse into the pores of the surface interacting with it.
K. T. Yong et al, Synthesis and plasmonic properties of silver and gold nanoshells on polystyrene cores of different size and gold-silver core-shell nanostructures Colloids and Surface; A 290 (2006) 89-105, describe a method for the preparation of nanoshell of gold and silver on the surfaces of polystyrene microspheres.
S T Kochuveedu et al, Surface-Plasmon induces visible light photocatalytic activity of TiO2 nanospheres decorated by Au nanoparticles with controlled configuration; J. Phys. Chem C 116, (2012) 2500-2506, describe a process for the decoration with gold nanoparticles of the surfaces of nano core-shell structures based on silicon oxide and titanium oxide.
However, conventional methods, based on the direct interaction of preformed nanoparticles prepared by chemical reduction with substrate surfaces, have shown several drawbacks such as the introduction of an additional chemical reducing agent and its subsequent removal step.
With this method, in order to allow a good interaction between the surface and the nanoparticles, it is crucial that the pre-formed metal nanoparticles have well-defined dimensions, namely less than the average size of the pores of the surface.
Conventional methods based on photochemical reactions for the preparation of metal nanodecorated surfaces are described in the following references:
U.S. Pat. No. 7,749,300 B2 (Chreien) describes a photochemical method for the production of core-shell bimetallic systems consisting of a metallic core of a first metal and a shell of a second metal. This method involves the mixing of the metal salts and chemical reducing agent;
U.S. Pat. No. 308,842 A1 describes a photochemical method for the preparation of nanodecorated surfaces; it is based on a photochemical modification of a polymeric monolayer previously deposited on the surface, containing a core-shell metal. This method involves several steps: deposition on the surface of a single layer of polymer containing the metal precursor, irradiation of the polymeric layer, removal of the polymeric layer by means of chemical agents;
Scirè S. et al (Supported silver catalysts prepared by deposition in aqueous solution of Ag nanoparticles Obtained through to photochemical approach; Applied Catalysis A 367 (2009) 138-145), describe a photochemical method for the preparation of substrates of Titania and Ceria with their surface decorated with silver nanoparticles, through the interaction of the substrate with photochemical pre-formed nanoparticles.
Photochemical methods for the direct decoration of surfaces are reported in the literature. For example, L. Costanzo in 2003 and S. Giuffrida in 2004 reported a direct photochemical method for the deposition of metal on hydrophilic substrates, such as quartz and silicon oxide, through the formation of nanostructured interconnected films. This method provides for the preparation of surfaces completely covered with homogeneous metallic films. No interaction between metal precursor and surface was reported, and that method does not allow the preparation of isolated, not interconnected and well anchored nanoparticles (G G Condorelli, L L Costanzo, I L Fragalá, S. Giuffrida and G. Ventimiglia, J. of Mater. Chem. 13 (2003) 2409-2411; S. Giuffrida, G G Condorelli, L L Costanzo, I L Fragalá, G. and G. Ventimiglia Old Chem. Mater. 16 (2004) 1260-1266).
In 2009, N. Luo et al reported a photochemical method for the deposition of metal nanoparticles on hydrophilic substrates (SiO2 microspheres) starting from polar precursors (ammonium salts). This method shows the formation of silver nanoparticles in the surface proximity and their subsequent deposition without direct interaction between metal precursor and surface (N. Luo, L. Mao, L. Jiang, Z. Wu, D. Wu, Material Letters 63 (2009) 154-156).
At present, no method is reported in literature that allows a selective decoration of a substrate according to its hydrophilic and hydrophobic properties.